Shared Libraries not linking together after installation with CMake - linux

Question

I have run into a rather strange problem with Google Tests.
In my project, I am using externalProject_add in order to download google tests and add them into my project. In my function, I believe I am asking for the project to be built, and then installed into a specific directory:
ExternalProject_Add(gTest_download
URL ${GTEST_url}
URL_HASH ${GTEST_hash}
UPDATE_COMMAND ""
BUILD_COMMAND cmake --build . --target install
CMAKE_CACHE_ARGS
-DCMAKE_C_COMPILER:PATH=${Compiler_C}
-DCMAKE_CXX_COMPILER:PATH=${Compiler_CXX}
-DBUILD_SHARED_LIBS:BOOL=ON
-DCMAKE_INSTALL_PREFIX:PATH=<BINARY_DIR>/installation
)
I can then tell the program where all the source files are living with this:
ExternalProject_Get_Property(gTest_download BINARY_DIR)
set(gTest_LIBRARY_DIR ${BINARY_DIR}/installation/lib CACHE INTERNAL "Google Test Binary Dir")
set(gTest_INCLUDE_DIR ${BINARY_DIR}/installation/include CACHE INTERNAL "Google Test Include Dir")
However, when I try to run a cmake test with protobufs I get the run time error:
./Protobuf_test: error while loading shared libraries: libgmock.so.1.11.0: cannot open shared object file: No such file or directory
Which is super odd, because I know I specifically told the program where to find the libraries in the same externalProject_add file:
set(gTest_LIBRARIES
${gTest_LIBRARY_DIR}/${prefix}gmock${suffix}
${gTest_LIBRARY_DIR}/${prefix}gmock_main${suffix}
${gTest_LIBRARY_DIR}/${prefix}gtest${suffix}
${gTest_LIBRARY_DIR}/${prefix}gtest_main${suffix}
CACHE INTERNAL "Google Test Libraries"
)
Where ${prefix} is "lib" and ${suffix} is ".lib". And I make sure to link them in my CMakeLists.txt file properly by doing target_link_libraries(Protobuf_test ${gTest_LIBRARIES} ${protobuf_LIBRARIES}) ex:
CUSTOM_PROTOBUF_GENERATE_CPP(PROTO_SRCS PROTO_HDS ${CMAKE_CURRENT_LIST_DIR} hello.proto)
include_directories(
${protoBuf_INCLUDE_DIR}
${gTest_INCLUDE_DIR}
${CMAKE_CURRENT_LIST_DIR}
)
add_executable(Protobuf_test protobuf_test.cc ${PROTO_SRCS} ${PROTO_HDS})
add_dependencies(Protobuf_test
gTest_download
protoBuf_download
)
target_link_libraries(Protobuf_test
${gTest_LIBRARIES}
${protoBuf_LIBRARIES}
)
add_test(NAME testing_protobuf COMMAND Protobuf_test)
So I went into the installation folder which is located in d/linuxBuild/lib/src/gTest_download-build/installation/lib and confirmed it exists there. I then ran ldd libgmock.so and got the following output:
libgtest.so.1.11.0 => not found
Which I thought was odd as well. gtest is in the same directory! How is that possible? So I ran ldd on gmock_main:
libgmock.so.1.11.0 => not found
libgtest.so.1.11.0 => not found
So now I have two libraries that are in the same directory however they cannot be found. Confused, I decide to go to where the libraries should have originally installed to and copied over from. So two folders up: d/linuxBuild/lib/src/gTest_download-build. I then go into that folders lib folder and verify the libraries are there. I then run the same ldd command on gmock:
libgtest.so.1.11.0 => /mnt/d/linuxBuild/lib/src/gTest_download-build/lib/libgtest.so.1.11.0 (0x00007fb651729000)
I'm confused by this and again, run it on gmock_main:
libgmock.so.1.11.0 => /mnt/d/linuxBuild/lib/src/gTest_download-build/lib/libgmock.so.1.11.0 (0x00007f58b0db3000)
libgtest.so.1.11.0 => /mnt/d/linuxBuild/lib/src/gTest_download-build/lib/libgtest.so.1.11.0 (0x00007f58b0c9c000)
I am sorry for the lengthy question, but I need to know what happened here? Why is it when I install the libraries the links break from each other and they don't know their locations compared to the ones in the original installation path? Did their symbolic links break? Did I do something incorrectly in the CMake build? I'm scratching my head on this problem since I have never encountered this before. Any advice would be greatly appreciated.

Answer 1

Forget about externalProject_add and use FetchContent / FetchContent_MakeAvailable, especially when dealing with CMake-ready projects:
See https://cmake.org/cmake/help/latest/module/FetchContent.html for details
include(FetchContent)
FetchContent_Declare(
googletest
GIT_REPOSITORY https://github.com/google/googletest.git
GIT_TAG release-1.11.0
)
FetchContent_MakeAvailable(googletest)
# ...
target_link_libraries(Protobuf_test
PRIVATE
gmock_main
${protoBuf_LIBRARIES}
)
This way, you are linking against the gmock_main target, which will set up your libraries, includes, and any indirect dependencies correctly like any cmake project added via add_subdirectory() or find_package().